Monochrome image sensor arrays typically comprise a linear array of photosensors which raster scan an image bearing document and convert the reflected light from each microscopic image area viewed by each photosensor over time to image signal charges. Following an integration period, the image signals are amplified and transferred to a common output line or bus through successively actuating multiplexing transistors.
In a well-known design of a photosensitive device such as used in an image input scanner, separate linear arrays of photosensors are arranged in parallel on a single sensor bar, and caused to move in a scan direction relative to the original image generally perpendicular to the direction of the arrays. The photosensors in each array are provided with a filter thereon of one primary color. As the sensor bar including the three rows of photosensors moves along the original image, each portion of the area of the original image is exposed to each of the rows of photosensors. As each filtered row of photosensors moves past each particular area in the original image, signals according to the different primary color separations of that area are output by the particular photosensors in each row. In this way, three separate sets of signals, each relating to one primary color, will be produced by the linear arrays of photosensors.
In practical applications of full-color input scanner arrays, the original documents or images which are typically scanned in can be roughly divided into two types: relatively sophisticated color images, such as color photographs, wherein a maximal amount of color information from the original is desirable, and from which information may be highly random; and simpler color images, such as those known as “highlight color” or “business color” images, in which the color relationships in the original image are not very complicated. For example, in a typical business document, the color portion of an image could be no more sophisticated than a color graph or pie-chart. Further, it is typical in business color or highlight color documents that the tone or shade of a particular color is consistent throughout a single graphic illustration. The fact that such highlight-color documents are fairly common in business presents opportunities for significantly increasing the efficiency at which original images can be converted into digital data, such as by decreasing the amount of digital memory space required to retain the image data, provided it is known in advance that the incoming document is of the business-color or highlight-color type.
There are typically two types of images which are recorded in document scanning: text, and images. With text, the sharpness of the recorded image, which relates to the spatial resolution of the recording process, is desirably maximized. With images such as photographs, however, sharpness may not be as much of a premium. Even where complicated images such as full-color photographs are being recorded, there may be disadvantages to obtaining a maximal amount of color data from an original image. Large amounts of image data from a scanner may impact process speed and/or data capacity of downstream memory. In many cases, it is possible that only a portion of the total information from the original image is required to reconstruct the image in a satisfactory manner.
The present invention is directed to photosensor configurations of photosensitive devices for recording full-color images, in which photosensors for recording different primary colors have different spatial resolutions.